MAMAMOO's Whee In has dropped "In Your Days" for the 'Thirty-Nine' OST.

The music video depicts same-aged friends Cha Mi Jo (played by Son Ye Jin), Jeong Chan Young (Jeon Mi Do), and Jang Joo Hee (Kim Ji Hyun) as they experience life, love, and loss together. "In Your Days" is an acoustic ballad about being by someone's side through good times and hard times. 

Listen to Whee In's "In Your Days" above, and let us know what you think in the comments below. Have you been watching 'Thirty-Nine'?